А) (15-7х)(15+7х)=225-49х²
б)(6m+9c)(6m-9c)=36m²-81c²
в)(5a^4-11b^7)(5a^4+11b^7)=25a^8-121b^14
г)(13p²-11m²)(11m²+13p²)=169p^4-121m^4
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Sin(-240°) = -sin240° = - sin(180 + 60) = sin60° = √3/2
cos(-240°) = cos240° = cos(180 + 60) = -cos60° = 1/2
tan(-240°) = -tan240° = -tan(180+60) = -tan60° = -√3
cot(-240°) = -cot240° = -cot(180+60) = -cot60° = -1/√3